This invention relates to telecommunication networks and more particularly to a method of quantifying the quality of spare links in a telecommunications network provisioned for distributedly restoring disrupted traffic.
In a telecommunications network provisioned with a distributed restoration algorithm (DRA), when a failure occurs at one of the links or nodes of the network, traffic that is traversing across the malfunctioned link or node is disrupted. In response to such failure, a DRA network will find alternate paths for rerouting the disrupted traffic. The finding of such alternate paths depends on the availability of any spare links immediately after the detection of the failure. The distributed restoration algorithm provides for a real time assessment of the spare topology of the network so that the optimal alternate paths may be ascertained irrespective of the type of topology the network encompasses.
As spare links are found for forming the alternate paths, prior to the instant invention, all spare links are presumed to be equivalent in terms of subsequent reliability. But given that the DRA network acts very quickly following a failure and therefore does not have the time to monitor the integrity of the spare link for any length of time before switching the traffic, there are instances where a DRA provisioned network may select some restoration paths which may subsequently fail. If anything, by routing traffic onto a restoration path that does not have the requisite reliability, the disruptive effects of the original failure are compounded.
A method therefore is required for a network provisioned with a DRA to readily identify any links that may appear to be intact but in actuality are susceptible to failure shortly after the restoration switching has been completed. Putting it differently, there is a need to incorporate into the DRA of the network a method for determining the reliability of the spare links of the network.
To better determine the reliability of spare links in a DRA telecommunications network, the present invention enhancement to the DRA is a process whereby the spare links of the network are categorized according to their respective anticipated near term reliability. In particular, not meaning to be inclusive, the following categories are prescribed. Spare links that are a part of functioning spans are preferred over spare links in spans which include other links that have failed. Also, spare links that are meant to be dedicated replacement links for working links within the DTNR domain are preferred over those spare links that are able to be preempted by line protection systems, i.e., non-DRA protection switching.
Thus, as envisioned, a spare link in a span that is dedicated as a replacement link for failed working links inside the DTNR domain in a span not associated therewith would be quantified to have the highest quality. The next quality spare link is one that is also not in the same span as the failed link but is located within a span that has the potential to be preempted by a line protection system. Another category involves spare links that are a part of the span that includes a failed working link and that acts as a dedicated replacement for failed working links within the DTNR domain. The final category involves spare links that are a part of a span that includes a failed working link. These spare links are located within a span that may be preempted by a line automatic protection system. Note that all spares act as a replacement for any one of the number of working links.
To determine that a spare link lies within a partially failed span, the sender node of the DRA provisioned network would dispatch to all spare links connected thereto a special message or signal that indicates that it is a custodial node with respect to a failed span. This signal may be propagated as part of a C bit keep alive message in accordance with the aforenoted application Ser. No. 60/099,582. The other of the custodial nodes that receives the special message along a given spare link is provisioned to assume that the spare link is a part of the failed span. Further provisioned is the logic that within any span that has suffered partial failure, the remaining links have a high likelihood of subsequent failure. By extension, it is further contemplated that the following spare links are even more prone to subsequent failure: spare links within spans where only working links have failed, and spare links within spans where other spare links, in addition to working links, have failed.
It is therefore an objective of the present invention to catagorize spare links into different quality levels based upon their respective anticipated near term availabilities in a DRA telecommunications network.
It is another objective of the present invention to ensure that robust spare links be used to restore traffic subsequent to a failure in a DRA network so that the disruptive effects of a first failure are not magnified.